X-ray fluorescence spectrometry often requires the sample to be in a homogeneous powdered form with a planar surface. Although this can be accomplished by spreading the powder on the window film of a cell designed for liquid samples (such as a SPEX SamplePrep X-Cell), comp-ression of the powder in a pellet die yields a denser, flatter surface that provides greater analytical accuracy and sensitivity, especially for wavelength XRF.

There are many different procedures for preparing powdered samples for XRF analysis. Typically, however, a representative quantity of the sample is first pulverized, then split to obtain enough powder for an XRF sample disc, usually 6 to 10 grams. That powder is blended with a binder if necessary, and placed in a pellet die (with or without a Spec-Cap) to be pressed into a sample disc which will hold together and has a flat, compositionally uniform surface. This disc is then placed in the sample holder of the XRF spectrometer.

An alternate technique, particularly useful when only a small amount of sample is available, incorporates a thin layer of sample on a binder pellet. The SPEX SamplePrep Sleeve-and-Plunger set, used with the appropriate pellet die, makes this procedure easy.

In the end, an exact procedure must be developed for each type of sample. The sampling method and the amount of sample to be ground, the type of mill and the grinding time, what size of die and what pressure to use, whether to include a binder or press the disc in a Spec-Cap, all these details may vary and must be worked out by the analyst to suit his or her samples, equip-ment, and analytical requirements. Running a series of standards or known samples will help to confirm that your chosen procedure results in accurate, reproducible data.